The various embodiments relate to ultrasonic flow meters and particularly to transducer assemblies used in ultrasonic flow meters.
After hydrocarbons have been removed from the ground, the fluid stream (either in a liquid phase or a gaseous phase) is transported from place to place via pipelines. It is desirable to know with accuracy the amount of fluid flowing in the stream, and particular accuracy is demanded when the fluid is changing hands, or during “custody transfer.” Even where custody transfer is not taking place, however, measurement accuracy is desirable, and in these situations ultrasonic flow meters may be used.
An ultrasonic flow meter includes two or more transducer assemblies, each secured inside of a port in the body, or spool piece, of the flow meter. To contain the transported fluid within the flow meter, an end connector is secured over the exterior end of each transducer port in the spool piece. Thus, the spool piece and end connectors create a pressure boundary that contains fluid flowing through the meter. To measure fluid flow through the meter, a pair of transducer assemblies is positioned along the inner surface of the spool piece, such that each transducer assembly faces the other. Each transducer assembly includes a piezoelectric element, and when an alternating current is applied to the piezoelectric element of the first transducer assembly, the piezoelectric element responds by radiating an ultrasonic wave in the fluid being transported through the flow meter. When the wave is incident upon the piezoelectric element of the second transducer assembly, that transducer assembly responds by generating an electric signal. Some time later, an alternating current is applied to the piezoelectric element of the second transducer assembly, and the piezoelectric element responds by radiating an ultrasonic wave through the fluid in the flow meter. When the wave is incident upon the piezoelectric element of the first transducer assembly, that transducer assembly responds by generating an electric signal. In this way, the transducer assemblies transmit and receive signals back and forth across the fluid stream.
Each transducer assembly is connected to a cable that extends through the end connector to the exterior of the spool piece and a remote location, such as an electronics base enclosure typically mounted to the exterior of the spool piece. The cable carries the signal created by the piezoelectric elements to an acquisition board positioned within the electronics base enclosure, where the signal may be processed and subsequently used to determine the fluid flow rate through the meter.
When not in use, the piezoelectric elements in the transducer assemblies can build up an electrical charge. The electric charge presents a hazard to personnel performing maintenance on the flow meter. To reduce the risk to maintenance personnel, each piezoelectric element is typically coupled to a transformer, which, in addition to functions discussed below, provides a discharge path for an electrical charge created by the piezoelectric element.
The transformer also provides impedance matching between the piezoelectric element and an acquisition device that ultimately receives the signal generated by the piezoelectric element. Thus, the piezoelectric element and the transformer are paired. Consequently, the transformer is typically positioned within the transducer assembly. With most conventional designs, when either the piezoelectric element or the transformer requires replacement, the entire transducer assembly is removed from the port in the spool piece, often necessitating an undesirable interruption in fluid flow through the spool piece when the end connector is removed to access the transducer assembly.
Further, in many conventional transducer assemblies, the transformer within the transducer assembly and/or electrical connections between the transformer and the piezoelectric element are susceptible to exposure to the same conditions as those experienced by the piezoelectric element. Such exposure is undesirable when the transformer or electrical connections are not designed for the same conditions as the piezoelectric element. For example, the fluid passing through the flow meter may be corrosive. While the piezoelectric element may be compatible with corrosive conditions, the transformer may not. In such circumstances, the corrosive fluid may damage the transformer and associated electrical wiring.
Mechanisms which improve the quality of the ultrasonic signals imparted to the fluid may improve measurement accuracy. Moreover, wear, tear, and component degradation (e.g., caused by the corrosivity of the fluid being measured) on the components of the meter can substantially decrease longevity of the device, and thus any apparatus, methods or systems that increase the durability and/or longevity of the flow meter and its components would be desirable. Finally, ultrasonic flow meters may be installed in harsh environments, and thus any mechanism to reduce maintenance time, and if possible improve performance, would be desirable.